1. Field of the Invention
The present invention relates to a spiral wound type membrane element employed for a membrane separation device such as a low-pressure reverse osmosis membrane separation device, an ultrafiltration device or a microfiltration device and methods of running and washing a spiral wound type membrane module.
2. Description of the Background Art
With recent applications of the membrane separation technology to water purification, the membrane separation technology is now applied as pretreatment for reverse osmosis membrane separation systems used desalination of seawater, for example. While a microfiltration membrane and an ultrafiltration membrane attaining high permeate flow rates are generally used for such membrane separation, a reverse osmosis membrane attaining a high permeate flow rate under ultra-low pressures of not more than 10 kgf/cm2 has recently been developed.
As a membrane element used for membrane separation, a hollow fiber membrane element is generally used in consideration of the membrane area (volumetric efficiency) per unit volume. However, the membranes of the hollow fiber membrane element are easy to break, and when the membranes are broken, raw water is mixed into the permeate to disadvantageously lower the separating performance.
On the other hand, a spiral wound type membrane element can provide a large membrane area. The spiral wound type membrane element, which can maintain high separating performance, is superior in reliability to the hollow fiber membrane element.
FIG. 19 is a partially fragmented perspective view of a conventional spiral wound type membrane element 21, and FIG. 20 is a perspective view showing the appearance of the conventional spiral wound type membrane element 21.
As shown in FIG. 19, the spiral wound type membrane element 21 is formed by superposing separation membranes 26 on both surfaces of a permeate spacer (permeate passage forming member) 25 and bonding three sides thereby forming an envelope-like membrane (bag-like membrane) 23, mounting an opening of the envelope-like membrane 23 on a water collection pipe 22 formed by a perforated hollow pipe and spirally winding the envelope-like membrane 23 on the outer peripheral surface of the water collection pipe 22 with a netty raw water spacer (raw water passage forming member) 24.
The raw water spacer 24 is provided for forming a passage for the raw water along the envelope-like membrane 23. If the thickness of the raw water spacer 24 is small, the separation membranes 26 are clogged with suspended substances although the charging efficiency thereof is increased. In general, therefore, the thickness of the raw water spacer 24 is set to about 0.7 to 3.0mm.
In relation to treatment of raw water such as river water containing a large quantity of suspended substances, a spiral wound type membrane element employing a zigzag corrugated sheet type raw water spacer (the so-called corrugated spacer) is already known in the art.
As shown in FIG. 20, the outer peripheral surface of the spiral wound type membrane element 21 is covered with a protective sheath 27 made of FRP (Fiber-Reinforced Plastics) or formed by a shrink tube, while packing holders 28 called anti-telescopes are mounted on both ends thereof respectively.
FIG. 21 is a sectional view showing an exemplary method of running the conventional spiral wound type membrane element 21. As shown in FIG. 21, a pressure vessel (pressure-resistant vessel) 30 is formed by a tubular case 31 and a pair of end plates 32a and 32b. The end plate 32a is provided with a raw water inlet 33, and the other plate 32b is provided with a concentrate outlet 35. The end plate 32b is provided on its center with a permeate outlet 34.
The spiral wound type membrane element 21 having a packing 37 mounted on a portion close to an end of the outer peripheral surface is introduced into the tubular case 31, and both opening ends of the tubular case 31 are sealed with the end plates 32a and 32b respectively. One opening end of the water collection pipe 22 is engaged with the permeate outlet 34 of the end plate 32b, while an end cap 36 is attached to the other opening end thereof.
In order to run the spiral wound type membrane element 21, raw water 51 is introduced into a first liquid chamber 38 from the raw water inlet 33 of the pressure vessel 30. As shown in FIG. 21, the raw water 51 is supplied from one end of the spiral wound type membrane element 21. The raw water 51 axially flows along the raw water spacer 24, and is discharged as concentrate 53 from the other end of the spiral wound type membrane element 21. The raw water 51 permeating through the separation membranes 26 along the raw water spacer 24 flows into the water collection pipe 22 as permeate 52 along the permeate spacer 25, and is discharged from the end of the water collection pipe 22.
The permeate 52 is taken out from the permeate outlet 34 of the pressure vessel 30 shown in FIG. 21. The concentrate 53 is taken out from a second liquid chamber 39 of the pressure vessel 30 through the concentrate outlet 35.
When the spiral wound type membrane element 21 is run, the membrane 23 is clogged with suspended substances contained in the raw water 51, to reduce the membrane flux. Therefore, chemical washing is performed for eliminating such clogging and recovering the membrane flux. However, such chemical washing requires much labor and a high cost. In order to prevent clogging, therefore, back wash reverse filtration is periodically performed with permeate or air in a hollow fiber membrane element, for example.
In the conventional spiral wound type membrane element 21, however, back wash reverse filtration results in the following problems:
FIG. 22 is a partially fragmented perspective view showing back wash reverse filtration in the conventional spiral wound type membrane element 21. As shown in FIG. 22, the permeate 52 is introduced from an end of the water collection pipe 22. Since the outer peripheral surface of the envelope-like membrane 23 wound around the water collection pipe 22 is covered with the protective sheath 27, the permeate 52 derived from the outer peripheral surface of the water collection pipe 22 permeates through the envelope-like membrane 23 and axially flows in the spiral wound type membrane element 21 along the raw water spacer 24, and is discharged from the end of the spiral wound type membrane element 21. Despite back wash reverse filtration, therefore, contaminants such as turbid substances causing clogging of the membrane 23 are readily captured by the raw water spacer 24 before discharged from the end of the spiral wound type membrane element 21 and insufficiently removed.
As shown in FIG. 21, further, the clearance between the inner peripheral surface of the tubular case 31 of the pressure vessel 30 and the spiral wound type membrane element 21 defines a dead space S, to cause residence of the fluid (fluid residue). When the spiral wound type membrane element 21 is used over a long period, the fluid residing in the dead space S is denatured. Particularly when the fluid contains organic matter, germs such as microorganisms may propagate to decompose the organic matter and give off a bad smell or decompose the separation membranes 26, leading to reduction of reliability.
In addition, the raw water 51 is supplied from one end of the conventional spiral wound type membrane element 21 and discharged from the other end, and hence the conventional spiral wound type membrane element 21 requires the packing holders 28 for prevent the envelope-like membrane 23 wound around the water collection pipe 22 from being deformed in the form of a bamboo shoot. Further, pressure loss caused by the raw water spacer 24 as well as by clogging results in pressure difference between the raw water inlet side and the concentrate outlet side, to deform the spiral wound type membrane element 21. In order to prevent such deformation, the outer peripheral surface of the envelope-like membrane 23 wound around the water collection pipe 22 is covered with the protective sheath 27 made of FRP or formed by a shrink tube. Thus, the component cost and the manufacturing cost are increased.
In order to prevent formation of cake with contaminants contained in the raw water 51, further, it is necessary to attain a sufficient linear velocity on the membrane surface with a sufficient flow rate on the concentrate side. When the flow rate is increased on the concentrate side, however, recovery per spiral wound type membrane element is reduced while a large pump is required for supplying the raw water 51, to remarkably increase the system cost.
An object of the present invention is to provide a highly reliable spiral wound type membrane element which can reduce the cost and is easy to wash, and a method of running a spiral wound type membrane module.
Another object of the present invention is to provide a washing method capable of readily and reliably removing contaminants captured by a spiral wound type membrane element.
In a method of running a spiral wound type membrane element according to an aspect of the first invention, the spiral wound type membrane element comprises a spiral membrane component including a perforated hollow pipe, a plurality of independent or continuous envelope-like membranes wound around the outer peripheral surface of the perforated hollow pipe and a raw liquid passage forming member interposed between the plurality of envelope-like membranes, a liquid-permeable material covering the outer peripheral portion of the spiral membrane component and an outer peripheral passage forming member entirely or partially covering the outer peripheral surface of the liquid-permeable material, and the method comprises a step of supplying a raw liquid having a function of separating contaminants or a bactericidal action from at least the outer peripheral side of the spiral wound type membrane element and taking out a permeated liquid from at least one opening end of the perforated hollow pipe in filtration running.
According to the method of running a spiral wound type membrane element, the raw liquid is supplied from at least the outer peripheral side of the spiral wound type membrane element in running for performing dead end filtration. In this case, contaminants are captured on at least the outer peripheral portion of the spiral wound type membrane element.
No dead space is defined in the clearance between the spiral wound type membrane element and the pressure vessel due to dead end filtration, to allow no residence of a fluid in the clearance between the spiral wound type membrane element and the pressure vessel. Also when employing the spiral wound type membrane element for separating a fluid containing organic matter, therefore, high reliability can be attained with no problems such as propagation of germs such as microorganisms, occurrence of a bad smell resulting from decomposition of organic matter and decomposition of separation membranes.
Further, the raw liquid is supplied from at least the outer peripheral side of the spiral wound type membrane element and pressure is applied to the spiral wound type membrane element from all directions with no pressure causing axial displacement, whereby the envelope-like membranes wound around the perforated hollow pipe are not deformed in the form of bamboo shoots. Thus, neither packing holders nor a protective sheath is required, whereby the component cost and the manufacturing cost are reduced. In addition, dead end filtration is performed for attaining high recovery without employing a large pump for supplying the raw liquid. Thus, the system cost is reduced.
The spiral wound type membrane element, to which pressure is applied from all directions, is not deformed also when the raw liquid is supplied under high pressure. Thus, high pressure resistance is attained.
Contaminants can be inhibited from adhering to at least the outer peripheral portion of the spiral wound type membrane element by supplying the spiral wound type membrane element with the raw liquid into which a chemical having a function of separating contaminants is injected.
Propagation of germs such as microorganisms can be suppressed on the membrane surface of the spiral wound type membrane element by supplying the spiral wound type membrane element with the raw liquid into which a chemical having a bactericidal action is injected.
Thus, the spiral wound type membrane element can be run over a long period.
The chemical may be sodium hypochlorite, chloramine, hydrogen peroxide, peracetic acid or ozone. Such a chemical having a function of separating contaminants can inhibit contaminants from adhering to at least the outer peripheral portion of the spiral wound type membrane element. Further, the chemical having a bactericidal action can suppress propagation of germs on the membrane surface.
The raw liquid may contain a flocculant. In this case, the flocculant flocculates contaminants contained in the raw liquid so that the contaminants are readily captured on at least the outer peripheral portion of the spiral wound type membrane element. Thus, loads on the envelope-like membranes are reduced to enable stable running over a long period.
The method may further comprise a step of introducing a washing liquid containing a chemical having a function of separating contaminants or a bactericidal action from at least one opening end of the perforated hollow pipe and discharging the washing liquid derived from the outer peripheral surface of the perforated hollow pipe at least through the outer peripheral portion of the spiral wound type membrane element.
When the washing liquid is introduced from at least one opening end of the perforated hollow pipe, the washing liquid derived from the outer peripheral surface of the perforated hollow pipe permeates through the envelope-like membranes and flows along the raw liquid passage forming member to be discharged from at least the outer peripheral portion of the spiral wound type membrane element. Thus, contaminants captured on at least the outer peripheral portion of the spiral wound type membrane element are separated from the spiral wound type membrane element. The liquid-permeable material and the outer peripheral passage forming member prevent the spiral wound type membrane element from spreading between the envelope-like membranes on the outer peripheral portion, thereby ensuring a passage for discharging contaminants adhering to at least the outer peripheral portion of the spiral wound type membrane element from the system in back wash reverse filtration. Therefore, the separated contaminants are discharged from the system with the washing liquid. Thus, the contaminants captured on at least the outer peripheral portion of the spiral wound type membrane element can be uniformly removed for regularly maintaining a stable permeate flow rate in running.
In this case, the chemical having a function of separating the contaminants contained in the washing liquid readily separates the contaminants adhering to at least the outer peripheral portion of the spiral wound type membrane element. Thus, the spiral wound type membrane element can be more effectively washed.
Further, the chemical having a bactericidal action contained in the washing liquid can more effectively suppress propagation of germs such as microorganisms on the membrane surface of the spiral wound type membrane element.
Thus, the spiral wound type membrane element can be stably run over a long period.
The washing liquid may be the permeated liquid.
The liquid-permeable material of the spiral wound type membrane element may be a separation membrane. In this case, the raw liquid is supplied from at least the outer peripheral side of the spiral wound type membrane element and the outer peripheral portion of the spiral membrane component is covered with the separation membrane, whereby contaminants are captured on the separation membrane on at least the outer peripheral portion of the spiral wound type membrane element. Therefore, the contaminants can be uniformly removed by back wash reverse filtration with permeate or the like, for example.
Further, only contaminants smaller than the pore size of the separation membrane on the outer peripheral portion infiltrate into the clearances between the envelope-like membranes forming the spiral membrane component, whereby loads on the envelope-like membranes are reduced to enable stable running over a long period.
In particular, the separation membrane may be a microfiltration membrane. In this case, contaminants larger than the pore size of the microfiltration membrane are captured on the outer peripheral portion of the spiral membrane component, not to infiltrate into the spiral membrane component.
The separation membrane may be an ultrafiltration membrane. In this case, contaminants larger than the pore size of the ultrafiltration membrane are captured on the outer peripheral portion of the spiral membrane component, not to infiltrate into the spiral membrane component.
The liquid-permeable material forming the spiral wound type membrane element may be a net. Even if contaminants captured on the outer peripheral portion of the spiral membrane component increase back pressure caused in back wash reverse filtration, the net forming the outer peripheral portion prevents the spiral membrane component from swelling, not to increase the spaces between the envelope-like membranes in this case. Thus, the envelope-like membranes are prevented from breakage resulting from swelling, so that contaminants contained in the raw liquid do not leak into the permeated liquid.
The net may be made of synthetic resin or metal.
The net preferably has at least three meshes and not more than 200 meshes. Thus, the spiral membrane component can be reliably inhibited from swelling caused by back pressure in back wash reverse filtration, and the raw liquid can be sufficiently supplied to the clearances between the envelope-like membranes forming the spiral membrane component from the outer peripheral side in running.
A prescribed portion of the net forming the outer peripheral portion of the spiral membrane component may be reinforced with resin along the circumferential direction. Thus, even if high back pressure is caused in back wash reverse filtration, the net forming the outer peripheral portion reliably prevents the spiral membrane component from swelling.
The permeate passage forming member inserted between the envelope-like membranes may extend outward from the outer peripheral side of the envelope-like membranes so that the extending portion of the permeate passage forming member is wound around the outer peripheral surface of the spiral membrane component as a net.
In this case, the spiral membrane component can be prevented from swelling caused by back pressure in back wash reverse filtration while suppressing an additional component cost.
The thickness of the outer peripheral passage forming member of the spiral wound type membrane element is preferably at least 0.6 mm and not more than 30 mm. Thus, contaminants adhering to at least the outer peripheral portion of the spiral wound type membrane element can be discharged from the system in back wash reverse filtration while keeping high volumetric efficiency of the spiral wound type membrane element with respect to the pressure vessel.
The outer peripheral passage forming member is preferably so arranged that the raw liquid substantially linearly flows substantially in parallel with the axial direction of the perforated hollow pipe. Thus, contaminants adhering to the outer peripheral portion of the spiral wound type membrane element can be substantially linearly washed away substantially in parallel with the axial direction of the perforated hollow pipe with the raw liquid with small pressure loss in back wash reverse filtration of the spiral wound type membrane element. Therefore, the contaminants adhering to the outer peripheral portion of the spiral wound type membrane element can be readily and reliably discharged from the system.
The outer peripheral passage forming member may be formed by a netty passage forming member. In this case, the netty passage forming member sufficiently protects the outer peripheral portion of the spiral wound type membrane element and prevents the spiral wound type membrane element from spreading between the envelope-like membranes on the outer peripheral portion. Further, the raw liquid can readily infiltrate into the clearances between the envelope-like membranes through the netty passage forming member from the outer peripheral portion of the spiral wound type membrane element. Thus, handleability of the spiral wound type membrane element is further improved and it is possible to efficiently supply the raw liquid between the envelope-like membranes while reliably capturing contaminants on the outer peripheral portion of the spiral wound type membrane element.
In a method of washing a spiral wound type membrane element according to another aspect of this invention, the spiral wound type membrane element comprises a spiral membrane component including a perforated hollow pipe, a plurality of independent or continuous envelope-like membranes wound around the outer peripheral surface of the perforated hollow pipe and a raw liquid passage forming member interposed between the plurality of envelope-like membranes, a liquid-permeable material covering the outer peripheral portion of the spiral membrane component and an outer peripheral passage forming member entirely or partially covering the outer peripheral surface of the liquid-permeable material, and the method comprises a step of supplying a washing liquid containing a chemical having a function of separating contaminants or a bactericidal action from at least one opening end of the perforated hollow pipe and discharging the washing liquid derived from the outer peripheral surface of the perforated hollow pipe from at least the outer peripheral portion of the spiral wound type membrane element.
In the aforementioned spiral wound type membrane element, at least the outer peripheral portion is not covered with a protective sheath but brought into an open state, whereby a raw liquid can be supplied from at least the outer peripheral side of the spiral wound type membrane element for performing dead end filtration. In this case, contaminants are captured on at least the outer peripheral portion of the spiral wound type membrane element.
When the washing liquid is introduced from at least one opening end of the perforated hollow pipe in washing, the washing liquid derived from the outer peripheral surface of the perforated hollow pipe permeates through the envelope-like membranes and flows along the raw liquid passage forming member, to be discharged from at least the outer peripheral portion of the spiral wound type membrane element. Thus, contaminants captured on at least the outer peripheral portion of the spiral wound type membrane element are separated from the spiral wound type membrane element and discharged from the system with the washing liquid. Thus, the contaminants captured on at least the outer peripheral portion of the spiral wound type membrane element can be uniformly removed.
In this case, the contaminants adhering to at least the outer peripheral portion of the spiral wound type membrane element can be readily separated by the chemical having a function of separating contaminants contained in the washing liquid. Thus, the spiral wound type membrane element can be more effectively washed.
Further, the chemical having a bactericidal action contained in the washing liquid can more effectively suppress propagation of germs such as microorganisms on the membrane surface of the spiral wound type membrane element.
Thus, the spiral wound type membrane element can be stably run over a long period.
The discharging step may include a step of dipping the spiral wound type membrane element in the washing liquid containing the chemical.
In this case, the washing liquid containing the chemical is introduced into the spiral wound type membrane element from the perforated hollow pipe for dipping the spiral wound type membrane element in the washing liquid for a prescribed time. In a spiral wound type membrane module formed by charging the spiral wound type membrane element in a pressure vessel, for example, the pressure vessel is filled with the washing liquid for dipping the spiral wound type membrane element therein. Thereafter the washing liquid is discharged from the system. Thus, contaminants adhering to at least the outer peripheral portion of the spiral wound type membrane element are readily separated due to such dipping and contaminants adhering to the membrane surface can also be readily washed out, whereby the spiral wound type membrane element can be more effectively washed. Further, it is possible to more effectively suppress propagation of germs such as microorganisms on the membrane surface of the spiral wound type membrane element.
Thus, the spiral wound type membrane element can be stably run over a long period.
The chemical may be sodium hypochlorite, chloramine, sulfuric acid, hydrochloric acid, sodium hydroxide, peracetic acid, isopropyl alcohol, oxalic acid or citric acid. Such a chemical having a function of separating contaminants can separate contaminants adhering to at least the outer peripheral surface for more effectively washing the spiral wound type membrane element. Further, the chemical having a bactericidal action can more effectively suppress propagation of germs on the membrane surface.
The discharging step may include a step of discharging the washing liquid from at least the outer peripheral portion of the spiral wound type membrane element and thereafter axially feeding a raw liquid along the outer peripheral portion of the spiral wound type membrane element. Thus, contaminants adhering to the outer peripheral portion of the spiral wound type membrane element can be readily separated and the contaminants separated from the spiral wound type membrane element can be readily and reliably discharged from the system.
Alternatively, the discharging step may include a step of axially feeding a raw liquid along the outer peripheral portion of the spiral wound type membrane element before introducing the washing liquid from at least one opening end of the perforated hollow pipe. Also in this case, contaminants adhering to the outer peripheral portion of the spiral wound type membrane element can be readily separated and the contaminants separated from the spiral wound type membrane element can be readily and reliably discharged from the system.
Alternatively, the discharging step may include a step of regularly or periodically axially feeding a raw liquid along the outer peripheral portion of the spiral wound type membrane element in parallel with introduction of the washing liquid from at least one opening end of the perforated hollow cylindrical pipe. Also in this case, contaminants adhering to the outer peripheral portion of the spiral wound type membrane element can be readily separated and the contaminants separated from the spiral wound type membrane element can be readily and reliably discharged from the system.
In a method of running a spiral wound type membrane module according to still another aspect of this invention, the spiral wound type membrane module comprises a pressure vessel having a raw liquid inlet and one or a plurality of spiral wound type membrane elements stored in the pressure vessel, the spiral wound type membrane element comprises a spiral membrane component including a perforated hollow pipe, a plurality of independent or continuous envelope-like membranes wound around the outer peripheral surface of the perforated hollow pipe and a raw liquid passage forming member interposed between the plurality of envelope-like membranes, a liquid-permeable material covering the outer peripheral portion of the spiral membrane component and an outer peripheral passage forming member entirely or partially covering the outer peripheral surface of the liquid-permeable material, and the method comprises a step of supplying a raw liquid containing a chemical having a function of separating contaminants or a bactericidal action at least from the outer peripheral side of the spiral wound type membrane element through the raw liquid inlet of the pressure vessel and taking out a permeated liquid from at least one opening end of the perforated hollow pipe in filtration running.
According to this method of running a spiral wound type membrane module, dead end filtration is performed during running. In this case, contaminants are captured on at least the outer peripheral portion of the spiral wound type membrane element.
No dead space is defined in the clearance between the spiral wound type membrane element and the pressure vessel due to dead end filtration, to allow no residence of the liquid in the clearance between the spiral wound type membrane element and the pressure vessel. Also when the spiral wound type membrane module is employed for separating a fluid containing organic matter, therefore, high reliability is attained with no problems such as propagation of germs such as microorganisms, occurrence of a bad smell resulting from decomposition of the organic matter, decomposition of separation membranes and the like.
Further, the spiral wound type membrane element requires neither packing holders nor a protective sheath, whereby the component cost and the manufacturing cost are reduced. In addition, high recovery is attained without employing a large pump for supplying the raw liquid due to dead end filtration. Thus, the system cost is reduced.
Further, the spiral wound type membrane element is supplied with the raw liquid into which the chemical having a function of separating contaminants is injected, whereby it is possible to inhibit contaminants from adhering to at least the outer peripheral portion of the spiral wound type membrane element.
In addition, the spiral wound type membrane element is supplied with the raw liquid into which the chemical having a bactericidal action is injected, whereby propagation of germs such as microorganisms can be suppressed on the membrane surface of the spiral wound type membrane element.
Thus, the spiral wound type membrane module can be stably run over a long period.
In a method of washing a spiral wound type membrane module according to a further aspect of this invention, the spiral wound type membrane module comprises a pressure vessel and one or a plurality of spiral wound type membrane elements stored in the pressure vessel, the spiral wound type membrane element comprises a spiral membrane component including a perforated hollow pipe, a plurality of independent or continuous envelope-like membranes wound around the outer peripheral surface of the perforated hollow pipe and a raw liquid passage forming member interposed between the plurality of envelope-like membranes, a liquid-permeable material covering the outer peripheral portion of the spiral membrane component and an outer peripheral passage forming member entirely or partially covering the outer peripheral surface of the liquid-permeable material, and the method comprises a step of supplying a washing liquid containing a chemical having a function of separating contaminants or a bactericidal action from at least one opening end of the perforated hollow pipe and discharging the washing liquid derived from the outer peripheral surface of the perforated hollow pipe through at least the outer peripheral portion of the spiral wound type membrane element for taking out the washing liquid from the pressure vessel.
When the washing liquid is introduced from at least one opening end of the perforated hollow pipe of the spiral wound type membrane element in the method of washing a spiral wound type membrane module, the washing liquid derived from the outer peripheral surface of the perforated hollow pipe permeates through the envelope-like membranes and flows along the raw liquid passage forming member to be discharged from at least the outer peripheral portion of the spiral wound type membrane element. Thus, contaminants captured on at least the outer peripheral portion of the spiral wound type membrane element are separated from the spiral wound type membrane element and discharged from the pressure vessel with the washing liquid. Thus, the contaminants captured on at least the outer peripheral portion of the spiral wound type membrane element can be uniformly removed.
In this case, the chemical having a function of separating contaminants contained in the washing liquid readily separates the contaminants adhering to at least the outer peripheral portion of the spiral wound type membrane element. Thus, the spiral wound type membrane element can be more effectively washed.
Further, the chemical having a bactericidal action contained in the washing liquid can more effectively suppress propagation of germs such as microorganisms on the membrane surface of the spiral wound type membrane element.
Thus, the spiral wound type membrane module can be stably run over a long period.
In a method of running a spiral wound type membrane element according to an aspect of the second invention, the spiral wound type membrane element comprises a spiral membrane component including a perforated hollow pipe, a plurality of independent or continuous envelope-like membranes wound around the outer peripheral surface of the perforated hollow pipe and a raw liquid passage forming member interposed between the plurality of envelope-like membranes, a liquid-permeable material covering the outer peripheral portion of the spiral membrane component and an outer peripheral passage forming member entirely or partially covering the outer peripheral surface of the liquid-permeable material, and the method comprises a step of continuously or intermittently diffusing bubbles in a liquid coming into contact with the outer peripheral portion of the spiral membrane component.
According to this method of running a spiral wound type membrane element, a diffused air flow is formed on the outer peripheral portion of the spiral wound type membrane element by diffusing bubbles in the liquid coming into contact with the outer peripheral portion of the spiral wound type membrane element. Thus, it is possible to inhibit contaminants contained in the liquid from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element. Further, it is possible to separate contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element.
Thus, the spiral wound type membrane element can be stably run over a long period.
In the aforementioned method of running a spiral wound type membrane element, no dead space is defined in the clearance between the spiral wound type membrane element and the pressure vessel due to dead end filtration, to allow no residence of the fluid in the clearance between the spiral wound type membrane element and the pressure vessel. Also when employing the spiral wound type membrane element for separating a fluid containing organic matter, therefore, high reliability can be attained with no problems such as propagation of germs such as microorganisms, occurrence of a bad smell resulting from decomposition of organic matter and decomposition of separation membranes.
Further, a raw liquid is supplied from at least the outer peripheral side of the spiral wound type membrane element and pressure is applied to the spiral wound type membrane element from all directions with no pressure causing axial displacement, whereby the envelope-like membranes wound around the perforated hollow pipe are not deformed in the form of bamboo shoots. Thus, neither packing holders nor a protective sheath is required, whereby the component cost and the manufacturing cost are reduced. In addition, high recovery is attained without employing a large pump for supplying the raw liquid, due to dead end filtration. Thus, the system cost is reduced.
In addition, pressure is applied to the spiral wound type membrane element from all directions, whereby the spiral wound type membrane element is not deformed even if the raw liquid is supplied under high pressure. Thus, high pressure resistance is attained.
In a method of running a spiral wound type membrane element according to another aspect of this invention, the spiral wound type membrane element comprises a spiral membrane component including a perforated hollow pipe, a plurality of independent or continuous envelope-like membranes wound around the outer peripheral surface of the perforated hollow pipe and a raw liquid passage forming member interposed between the plurality of envelope-like membranes, a liquid-permeable material covering the outer peripheral portion of the spiral membrane component and an outer peripheral passage forming member entirely or partially covering the outer peripheral surface of the liquid-permeable material, and the method comprises a step of continuously or intermittently applying ultrasonic vibration to a liquid coming into contact with the outer peripheral portion of the spiral membrane component.
According to this method of running a spiral wound type membrane element, contaminants contained in the liquid can be dispersed by applying ultrasonic vibration to the liquid coming into contact with the outer peripheral portion of the spiral membrane component for inhibiting the contaminants from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element. The spiral wound type membrane element also vibrates and hence it is possible to separate contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element.
Thus, the spiral wound type membrane element can be stably run over a long period.
In the aforementioned method of running a spiral wound type membrane element, no dead space is defined in the clearance between the spiral wound type membrane element and the pressure vessel due to dead end filtration, to allow no residence of a fluid in the clearance between the spiral wound type membrane element and the pressure vessel. Also when employing the spiral wound type membrane element for separating a fluid containing organic matter, therefore, high reliability can be attained with no problems such as propagation of germs such as microorganisms, occurrence of a bad smell resulting from decomposition of organic matter and decomposition of separation membranes.
Further, a raw liquid is supplied from at least the outer peripheral side of the spiral wound type membrane element and pressure is applied to the spiral wound type membrane element from all directions with no pressure causing axial displacement, whereby the envelope-like membranes wound around the perforated hollow pipe are not deformed in the form of bamboo shoots. Thus, neither packing holders nor a protective sheath is required, whereby the component cost and the manufacturing cost are reduced. In addition, high recovery is attained without employing a large pump for supplying the raw liquid due to dead end filtration. Thus, the system cost is reduced.
Further, pressure is applied to the spiral wound type membrane element from all directions, whereby the spiral wound type membrane element is not deformed even if the raw liquid is supplied under high pressure. Thus, high pressure resistance is attained.
In a method of running a spiral wound type membrane module according to still another aspect of this invention, the spiral wound type membrane module comprises a pressure vessel and one or a plurality of spiral wound type membrane elements stored in the pressure vessel, the spiral wound type membrane element comprises a spiral membrane component including a perforated hollow pipe, a plurality of independent or continuous envelope-like membranes wound around the outer peripheral surface of the perforated hollow pipe and a raw liquid passage forming member interposed between the plurality of envelope-like membranes, a liquid-permeable material covering the outer peripheral portion of the spiral membrane component and an outer peripheral passage forming member entirely or partially covering the outer peripheral surface of the liquid-permeable material, and the method comprises a step of continuously or intermittently diffusing bubbles in a liquid stored in the pressure vessel.
According to the method of running a spiral wound type membrane module, a diffused air flow is formed on the outer peripheral portion of the spiral wound type membrane element by diffusing bubbles in the liquid stored in the pressure vessel. Thus, it is possible to inhibit contaminants contained in the liquid from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element. Further, it is possible to separate contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element.
In the method of running a spiral wound type membrane module, no dead space is defined in the clearance between the spiral wound type membrane element and the pressure vessel due to dead end filtration, to allow no residence of a fluid in the clearance between the spiral wound type membrane element and the pressure vessel. Also when employing the spiral wound type membrane module for separating a fluid containing organic matter, therefore, high reliability is attained with no problems such as propagation of germs such as microorganisms, occurrence of a bad smell resulting from decomposition of the organic matter and decomposition of the separation membrane.
Further, a raw liquid is supplied from at least the outer peripheral side of the spiral wound type membrane element and pressure is applied to the spiral wound type membrane element from all directions with no pressure causing axial displacement, whereby the envelope-like membranes wound around the perforated hollow pipe are not deformed in the form of bamboo shoots. Thus, neither packing holders nor a protective sheath is required, whereby the component cost and the manufacturing cost are reduced. In addition, high recovery is attained without employing a large pump for supplying the raw liquid due to the dead end filtration. Thus, the system cost is reduced.
Further, pressure is applied to the spiral wound type membrane element from all directions, whereby the spiral wound type membrane element is not deformed even if the raw liquid is supplied under high pressure. Thus, high pressure resistance is attained.
As a first mode of the method of running a spiral wound type membrane module according to this invention, the step of diffusing bubbles may include a step of supplying a raw liquid from at least the outer peripheral side of the spiral wound type membrane element while diffusing bubbles in the raw liquid and taking out a permeated liquid from at least one opening end of the perforated hollow pipe in filtration running. In this case, contaminants contained in the raw liquid are captured on at least the outer peripheral portion of the spiral wound type membrane element.
A diffused air flow is formed on the outer peripheral portion of the spiral wound type membrane element by diffusing bubbles in the raw liquid. Thus, it is possible to inhibit contaminants contained in the raw liquid from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element and to separate contaminants adhering to the inner part of the spiral wound type membrane module, particularly to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element.
As a second mode of the method of running a spiral wound type membrane module according to this invention, the step of diffusing bubbles may include a step of introducing a washing liquid from at least one opening end of the perforated hollow pipe and discharging the washing liquid derived from the outer peripheral surface of the perforated hollow pipe through at least the outer peripheral portion of the spiral wound type membrane element while diffusing bubbles in the washing liquid in washing.
In washing, the washing liquid is introduced from at least one opening end of the perforated hollow pipe for performing back wash reverse filtration. The washing liquid derived from the outer peripheral surface of the perforated hollow pipe permeates through the envelope-like membranes and flows along the raw liquid passage forming member to be discharged from at least the outer peripheral portion of the spiral wound type membrane element. Thus, contaminants captured on the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element are separated from the spiral wound type membrane element. The liquid-permeable material and the outer peripheral passage forming member prevent the spiral wound type membrane element from spreading between the envelope-like membranes on the outer peripheral portion, thereby ensuring a passage for discharging contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element in back wash reverse filtration. Thus, the separated contaminants are discharged outward with the washing liquid. Therefore, the contaminants captured on the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element can be uniformly removed so that a constant permeate flow rate can be regularly maintained in running.
A diffused air flow is formed on the outer peripheral portion of the spiral wound type membrane element by diffusing bubbles in the washing liquid. Thus, it is possible to more effectively separate the contaminants adhering to the inner part of the spiral wound type membrane module, particularly to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element, and to inhibit the separated contaminants from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element.
As a third mode of the method of running a spiral wound type membrane module according to this invention, the step of diffusing bubbles may include a step of axially feeding a raw liquid or a washing liquid along the outer peripheral portion of the spiral wound type membrane element while diffusing bubbles in the raw liquid or the washing liquid in flushing. Thus, contaminants adhering to the inner part of the spiral wound type membrane module, particularly to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element can be readily separated and the separated contaminants can be readily and reliably discharged outward.
As a fourth mode of the method of running a spiral wound type membrane module according to this invention, the step of diffusing bubbles may include a step of diffusing bubbles in a raw liquid or a washing liquid stored in the pressure vessel when stopping running. In this case, a diffused air flow is formed on the outer peripheral portion of the spiral wound type membrane element. Thus, it is possible to inhibit contaminants contained in the raw liquid or the washing liquid from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element and to separate contaminants adhering to the inner part of the spiral wound type membrane module, particularly to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element.
The method may include a step of continuously or intermittently axially feeding a partial raw liquid along the outer peripheral portion of the spiral wound type membrane element and taking out the partial raw liquid from the pressure vessel in filtration running. In this case, it is possible to readily and reliably discharge part of contaminants contained in the raw liquid and contaminants separated from the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element from the spiral wound type membrane module and to further inhibit the contaminants contained in the raw liquid from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element. Thus, the spiral wound type membrane module can be further stably run continuously over a long period.
Further, the method may include a step of returning the raw liquid taken out from the pressure vessel to the supply side again. In this case, the discharged raw liquid is circulated, whereby the supplied raw liquid can be recovered as a permeated liquid with recovery of 100% in theory.
In a method of running a spiral wound type membrane module according to a further aspect of this invention, the spiral wound type membrane module comprises a pressure vessel and one or a plurality of spiral wound type membrane elements stored in the pressure vessel, the spiral wound type membrane element comprises a spiral membrane component including a perforated hollow pipe, a plurality of independent or continuous envelope-like membranes wound around the outer peripheral surface of the perforated hollow pipe and a raw liquid passage forming member interposed between the plurality of envelope-like membranes, a liquid-permeable material covering the outer peripheral portion of the spiral membrane component and an outer peripheral passage forming member entirely or partially covering the outer peripheral surface of the liquid-permeable material, and the method comprises a step of continuously or intermittently applying ultrasonic vibration to a liquid stored in the pressure vessel.
According to this method of running a spiral wound type membrane module, it is possible to discharge contaminants contained in the liquid stored in the pressure vessel for inhibiting the contaminants from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element by applying ultrasonic vibration to the liquid. The spiral wound type membrane element also vibrates, whereby contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element can be separated.
Thus, the spiral wound type membrane element can be stably run continuously over a long period.
In the aforementioned method of running a spiral wound type membrane module, no dead space is defined in the clearance between the spiral wound type membrane element and the pressure vessel due to dead end filtration, to allow no residence of a fluid in the clearance between the spiral wound type membrane element and the pressure vessel. Also when employing the spiral wound type membrane module for separating a fluid containing organic matter, therefore, high reliability is attained with no problems such as propagation of germs such as microorganisms, occurrence of a bad smell resulting from decomposition of the organic matter and decomposition of separation membranes.
Further, a raw liquid is supplied from at least the outer peripheral side of the spiral wound type membrane element and pressure is applied to the spiral wound type membrane element from all directions with no pressure causing axial displacement, whereby the envelope-like membranes wound around the perforated hollow pipe are not deformed in the form of bamboo shoots. Thus, neither packing holders nor a protective sheath is required, whereby the component cost and the manufacturing cost are reduced. Further, high recovery is attained without employing a large pump for supplying the raw liquid due to dead end filtration. Thus, the system cost is reduced.
In addition, pressure is applied to the spiral wound type membrane element from all directions, whereby the spiral wound type membrane element is not deformed even if the raw liquid is supplied under high pressure. Thus, high pressure resistance is attained.
As a fifth mode of the method of running a spiral wound type membrane module according to this invention, the step of applying ultrasonic vibration may include a step of supplying a raw liquid from at least the outer peripheral side of the spiral wound type membrane element while applying ultrasonic vibration to the raw liquid and taking out a permeated liquid from at least one opening end of the perforated hollow pipe in filtration running. In this case, contaminants contained in the raw liquid are captured on at least the outer peripheral portion of the spiral wound type membrane element.
It is possible to disperse the contaminants contained in the raw liquid and inhibit the contaminants from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element by applying ultrasonic vibration to the raw liquid. The spiral wound type membrane element also vibrates, whereby contaminants adhering to the inner part of the spiral wound type membrane module, particularly to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element can be separated.
As a sixth mode of the method of running a spiral wound type membrane module according to this invention, the step of applying ultrasonic vibration may include a step of introducing a washing liquid from at least one opening end of the perforated hollow pipe and applying ultrasonic vibration to the washing liquid while discharging the washing liquid derived from the outer peripheral surface of the perforated hollow pipe through at least the outer peripheral portion of the spiral wound type membrane element in washing. In washing, the washing liquid is introduced from at least one opening end of the perforated hollow pipe for performing back wash reverse filtration. The washing liquid derived from the outer peripheral surface of the perforated hollow pipe permeates the envelope-like membranes and flows along the raw liquid passage forming member, to be discharged from at least the outer peripheral portion of the spiral wound type membrane element. Thus, contaminants captured on the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element are separated from the spiral wound type membrane element. The liquid-permeable material and the outer peripheral passage forming member prevent the spiral wound type membrane element from spreading between the envelope-like membranes on the outer peripheral portion, thereby ensuring a passage for discharging contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element outward in back wash reverse filtration. Thus, the separated contaminants are discharged outward with the washing liquid. Therefore, the contaminants captured on the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element can be uniformly removed, and it is possible to regularly maintain a stable permeate flow rate in running.
It is possible to more effectively separate contaminants adhering to the inner part of the spiral wound type membrane module, particularly to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element and to inhibit the separated contaminants from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element by applying ultrasonic vibration to the washing liquid.
As a seventh mode of the method of running a spiral wound type membrane module according to this invention, the step of applying ultrasonic vibration may include a step of axially feeding a raw liquid or a washing liquid along the outer peripheral portion of the spiral wound type membrane element and applying ultrasonic vibration to the raw liquid or the washing liquid in flushing. Thus, contaminants adhering to the inner part of the spiral wound type membrane module, particularly to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element can be readily separated and the separated contaminants can be readily and reliably discharged outward.
As an eighth mode of the method of running a spiral wound type membrane module according to this invention, the step of applying ultrasonic vibration may include a step of applying ultrasonic vibration to a raw liquid or a washing liquid stored in the pressure vessel when stopping running. Thus, it is possible to inhibit contaminants contained in the raw liquid or the washing liquid from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element and to separate contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element.
The method may include a step of continuously or intermittently axially feeding a partial raw liquid along the outer peripheral portion of the spiral wound type membrane element and taking out the partial raw liquid from the pressure vessel. In this case, it is possible to readily and reliably discharge part of the contaminants contained in the raw liquid and contaminants separated from the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element from the spiral wound type membrane module, and to further inhibit the contaminants contained in the raw liquid from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element. Thus, the spiral wound type membrane module can be further stably run continuously over a long period.
The method may further include a step of returning the raw liquid taken out from the pressure vessel to the supply side again. In this case, the discharged raw liquid is circulated, whereby the supplied raw liquid can be recovered as a permeated liquid with recovery of 100% in theory.
A spiral wound type membrane module according to a further aspect of this invention comprises a pressure vessel having a raw liquid inlet and a raw water outlet and one or a plurality of spiral wound type membrane elements stored in the pressure vessel, the spiral wound type membrane element comprises a spiral membrane component including a perforated hollow pipe, a plurality of independent or continuous envelope-like membranes wound around the outer peripheral surface of the perforated hollow pipe and a raw liquid passage forming member interposed between the plurality of envelope-like membranes, a liquid-permeable material covering the outer peripheral portion of the spiral membrane component and an outer peripheral passage forming member entirely or partially covering the outer peripheral surface of the liquid-permeable material, and the spiral wound type membrane module further comprises an air diffuser diffusing bubbles in a liquid stored in the pressure vessel and a circulation system returning a raw liquid taken out from the pressure vessel through the raw liquid outlet to the raw liquid inlet.
In this spiral wound type membrane module, the air diffuser continuously or intermittently diffuses bubbles in the raw liquid or a washing liquid stored in the pressure vessel. Thus, a diffused air flow is formed on the outer peripheral portion of the spiral wound type membrane element in the spiral wound type membrane module, whereby contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element can be separated. Further, it is possible to inhibit contaminants contained in the raw liquid or the washing liquid and the separated contaminants from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element.
In running, it is possible to readily and reliably discharge part of the contaminants contained in the raw liquid and the separated contaminants from the spiral wound type membrane module and to further inhibit the contaminants contained in the raw liquid and the separated contaminants from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element by axially forming a flow of the raw liquid along the outer peripheral portion of the spiral wound type membrane element.
Thus, the spiral wound type module implements stable performance.
Further, the circulation system is provided for returning the raw liquid taken out from the pressure vessel through the raw liquid outlet to the raw liquid inlet again, whereby the supplied raw liquid can be recovered as a permeated liquid with recovery of 100% in theory.
In addition, no dead space is defined in the clearance between the spiral wound type membrane element and the pressure vessel to allow no residence of a fluid in the clearance between the spiral wound type membrane element and the pressure vessel due to dead end filtration. Also when employing the spiral wound type membrane module for separating a fluid containing organic matter, therefore, high reliability is attained with no problems such as propagation of germs such as microorganisms, occurrence of a bad smell resulting from decomposition of the organic matter and decomposition of separation membranes.
Further, the raw liquid is supplied from at least the outer peripheral side of the spiral wound type membrane element and pressure is applied to the spiral wound type membrane element from all directions with no pressure causing axial displacement, whereby the envelope-like membranes wound around the perforated hollow pipe are not deformed in the form of bamboo shoots. Thus, neither packing holders nor a protective sheath is required, whereby the component cost and the manufacturing cost are reduced. Further, high recovery is attained without employing a large pump for supplying the raw liquid due to dead end filtration. Thus, the system cost is reduced.
In addition, pressure is applied to the spiral wound type membrane element from all directions, whereby the spiral wound type membrane element is not deformed even if the raw liquid is supplied under high pressure. Thus, high pressure resistance is attained.
A spiral wound type membrane module according to a further aspect of this invention comprises a pressure vessel and one or a plurality of spiral wound type membrane elements stored in the pressure vessel, the spiral wound type membrane element comprises a spiral membrane component including a perforated hollow pipe, a plurality of independent or continuous envelope-like membranes wound around the outer peripheral surface of the perforated hollow pipe and a raw liquid passage forming member interposed between the plurality of envelope-like membranes, a liquid-permeable material covering the outer peripheral portion of the spiral membrane component and an outer peripheral passage forming member entirely or partially covering the outer peripheral surface of the liquid-permeable material, and the spiral wound type membrane module further comprises an ultrasonic oscillator applying ultrasonic vibration to a liquid stored in the pressure vessel.
In the spiral wound type membrane module, the ultrasonic oscillator continuously or intermittently applies ultrasonic vibration to a raw liquid or a washing liquid stored in the pressure vessel. Thus, the spiral wound type membrane element vibrates, whereby it is possible to separate contaminants adhering to the inner part of the spiral wound type membrane module, particularly to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element. Further, it is possible to inhibit contaminants contained in the raw liquid or the washing liquid and the separated contaminants from adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element. Thus, the spiral wound type membrane module implements stable performance.
In addition, no dead space is defined in the clearance between the spiral wound type membrane element and the pressure vessel to allow no residence of a fluid in the clearance between the spiral wound type membrane element and the pressure vessel due to dead end filtration. Also when employing the spiral wound type membrane module for separating a fluid containing organic matter, therefore, high reliability is attained with no problems such as propagation of germs such as microorganisms, occurrence of a bad smell resulting from decomposition of the organic matter and decomposition of separation membranes.
Further, the raw liquid is supplied from at least the outer peripheral side of the spiral wound type membrane element and pressure is applied to the spiral wound type membrane element from all directions with no pressure causing axial displacement, whereby the envelope-like membranes wound around the perforated hollow pipe are not deformed in the form of bamboo shoots. Thus, neither packing holders nor a protective sheath is required, whereby the component cost and the manufacturing cost are reduced. In addition, high recovery is attained without employing a large pump for supplying the raw liquid due to dead end filtration. Thus, the system cost is reduced.
Further, pressure is applied to the spiral wound type membrane element from all directions, whereby the spiral wound type membrane element is not deformed even if the raw liquid is supplied under high pressure. Thus, high pressure resistance is attained.
In a method of running a spiral wound type membrane element according to an aspect of this invention, the spiral wound type membrane element comprises a spiral membrane component including a perforated hollow pipe, a plurality of independent or continuous envelope-like membranes wound around the outer peripheral surface of the perforated hollow pipe and a raw liquid passage forming member interposed between the plurality of envelope-like membranes, a liquid-permeable material covering the outer peripheral portion of the spiral membrane component and an outer peripheral passage forming member entirely or partially covering the outer peripheral surface of the liquid-permeable material, and the method comprises a step of temporarily stopping running and holding the spiral wound type membrane element in a state dipped in a liquid for a prescribed time during a running period.
In this method of running a spiral wound type membrane element, at least the outer peripheral portion of the spiral wound type membrane element is not covered with a protective sheath but brought into an open state, whereby it is possible to separate contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element for recovering the membrane function of the spiral wound type membrane element by holding the spiral wound type membrane element in the state dipped in the liquid for the prescribed time. Thus, the spiral wound type membrane element can be stably run with high reliability. Such an operation can be readily performed with no requirement for particular equipment while the contaminants can be separated with no chemical for washing. Thus, the method can be carried out at a low cost.
As a first mode of the method of running a spiral wound type membrane element according to this invention, the holding step may include a step of supplying a raw liquid from at least the outer peripheral side of the spiral wound type membrane element while taking out a permeated liquid from at least one opening end of the perforated hollow pipe during filtration running in the running period and stopping the filtration running for holding the spiral wound type membrane element in the state dipped in the liquid for the prescribed time.
In this case, the raw liquid is supplied from at least the outer peripheral side of the spiral wound type membrane element while dead end filtration is performed so that contaminants are captured on at least the outer peripheral portion of the spiral wound type membrane element. Therefore, loads on the envelope-like membranes are reduced.
Further, no dead space is defined in the clearance between the spiral wound type membrane element and the pressure vessel to allow no residence of a fluid in the clearance between the spiral wound type membrane element and the pressure vessel due to dead end filtration. Also when employing the spiral wound type membrane module for separating a fluid containing organic matter, therefore, high reliability is attained with no problems such as propagation of germs such as microorganisms, occurrence of a bad smell resulting from decomposition of the organic matter and decomposition of separation membranes.
In addition, the raw liquid is supplied from at least the outer peripheral side of the spiral wound type membrane element and pressure is applied to the spiral wound type membrane element from all directions with no pressure causing axial displacement, whereby the envelope-like membranes wound around the perforated hollow pipe are not deformed in the form of bamboo shoots. Thus, neither packing holders nor a protective sheath is required, whereby the component cost and the manufacturing cost are reduced. Further, high recovery is attained without employing a large pump for supplying the raw liquid due to dead end filtration. Thus, the system cost is reduced.
In addition, pressure is applied to the spiral wound type membrane element from all directions, whereby the spiral wound type membrane element is not deformed even if the raw liquid is supplied under high pressure. Thus, high pressure resistance is attained.
Further, it is possible to separate contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound membrane element following filtration running by stopping filtration running and dipping the spiral wound type membrane element in the liquid for the prescribed time.
In the aforementioned method of running a spiral wound type membrane element, a partial raw liquid may be regularly or periodically fed axially along the outer peripheral portion of the spiral wound type membrane element. Thus, it is possible to inhibit contaminants contained in the raw liquid from adhering to at least the outer peripheral portion of the spiral wound type membrane element for further stably running the spiral wound type membrane element.
As a second mode of the method of running a spiral wound type membrane element according to this invention, the holding step may include a step of introducing a washing liquid from at least one opening end of the perforated hollow pipe while discharging the washing liquid derived from the outer peripheral surface of the perforated hollow pipe through at least the outer peripheral portion of the spiral wound type membrane element in back wash reverse filtration in the running period and stopping the back wash reverse filtration for holding the spiral wound type membrane element in the state dipped in the liquid for the prescribed time.
When the washing liquid is introduced from at least one opening end of the perforated hollow pipe, the washing liquid derived from the outer peripheral surface of the perforated hollow pipe permeates through the envelope-like membranes and flows along the raw liquid passage forming member, to be discharged from at least the outer peripheral portion of the spiral wound type membrane element. Thus, contaminants captured on the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element are separated from the spiral wound type membrane element. The liquid-permeable material and the outer peripheral passage forming member prevent the spiral wound type membrane element from spreading between the envelope-like membranes in the outer peripheral portion, thereby ensuring a passage for discharging contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element in back wash reverse filtration. Thus, the separated contaminants are discharged with the washing liquid. Therefore, it is possible to uniformly remove contaminants captured on the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element, and to regularly maintain a constant permeate flow rate in filtration running.
Further, it is possible to more effectively separate contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element following filtration by stopping back wash reverse filtration and dipping the spiral wound type membrane element in the liquid for the prescribed time.
The aforementioned first mode may further comprise a step of restarting filtration running after holding the spiral wound type membrane element in the state dipped in the liquid for the prescribed time. In this case, it is possible to separate contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element by dipping the spiral wound type membrane element in the liquid for the prescribed time, whereby high reliability and stability can be attained in the restarted filtration running.
Alternatively, the aforementioned first mode may further comprise a step of performing back wash reverse filtration by introducing a washing liquid from at least one opening end of the perforated hollow pipe while discharging the washing liquid derived from the outer peripheral surface of the perforated hollow pipe through at least the outer peripheral portion of the spiral wound type membrane element after holding the spiral wound type membrane element in the state dipped in the liquid for the prescribed time. In this case, back wash reverse filtration is performed after dipping the spiral wound type membrane element in the liquid for the prescribed time, whereby contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element can be readily and reliably separated. Thus, reliable and stable filtration running can be performed.
The aforementioned first mode may further comprise a step of performing flushing by axially feeding a raw liquid along the outer peripheral portion of the spiral wound type membrane element after holding the spiral wound type membrane element in the state dipped in the liquid for the prescribed time. In this case, contaminants adhering to the outer peripheral portion of the spiral wound type membrane element can be readily separated by flushing, while the contaminants separated from the spiral wound type membrane element can be readily and reliably discharged.
Alternatively, the aforementioned second mode may further comprise a step of supplying a liquid containing a chemical having a bactericidal action or a function separating contaminants to the spiral wound type membrane element and dipping the spiral wound type membrane element in the liquid containing the chemical after holding the spiral wound type membrane element in the state dipped in the liquid for the prescribed time. Thus, it is possible to exterminate germs propagating on the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element or to more effectively and reliably separate contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element.
The aforementioned second mode may further comprise a step of restarting back wash reverse filtration after holding the spiral wound type membrane element in the state dipped in the liquid for the prescribed time. In this case, the back wash reverse filtration is performed after dipping the spiral wound type membrane element in the liquid for the prescribed time, whereby contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element can be readily and reliably separated. Thus, reliable and stable filtration running can be performed.
Alternatively, the aforementioned second mode may further comprise a step of performing filtration running by supplying a raw liquid from at least the outer peripheral portion of the spiral wound type membrane element while taking out a permeated liquid from at least one opening end of the perforated hollow pipe after holding the spiral wound type membrane element in the state dipped in the liquid for the prescribed time. In this case, contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element can be separated by dipping the spiral wound type membrane element in the liquid for the prescribed time, whereby high reliability and stability are attained in filtration running after the dipping.
Alternatively, the aforementioned second mode may further comprise a step of performing flushing by axially feeding a raw liquid along the outer peripheral portion of the spiral wound type membrane element after holding the spiral wound type membrane element in the state dipped in the liquid for the prescribed time. In this case, contaminants adhering to the outer peripheral portion of the spiral wound type membrane element can be readily separated by flushing, while the contaminants separated from the spiral wound type membrane element can be readily and reliably discharged outward.
Alternatively, the aforementioned second mode may further comprise a step of supplying a liquid containing a chemical having a bactericidal action or a function separating contaminants to the spiral wound type membrane element and dipping the spiral wound type membrane element in the liquid containing the chemical after holding the spiral wound type membrane element in the state dipped in the liquid for the prescribed time. Thus, it is possible to exterminate germs propagating on the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element or to more effectively and reliably separate contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element.
In a method of running a spiral wound type membrane module according to a further aspect of this invention, the spiral wound type membrane module comprises a pressure vessel and one or a plurality of spiral wound type membrane elements stored in the pressure vessel, the spiral wound type membrane element comprises a spiral membrane component including a perforated hollow pipe, a plurality of independent or continuous envelope-like membranes wound around the outer peripheral surface of the perforated hollow pipe and a raw liquid passage forming member interposed between the plurality of envelope-like membranes, a liquid-permeable material covering the outer peripheral portion of the spiral membrane component and an outer peripheral passage forming member entirely or partially covering the outer peripheral surface of the liquid-permeable material, and the method comprises a step of temporarily stopping running and holding the spiral wound type membrane module in a state sealing a liquid in the pressure vessel for a prescribed time in a running period.
In this method of running a spiral wound type membrane module, at least the outer peripheral portion of the spiral wound type membrane element stored in the pressure vessel is not covered with a protective sheath but brought into an open state. Therefore, it is possible to separate contaminants adhering to the membrane surface and at least the outer peripheral portion of the spiral wound type membrane element and recover the membrane function of the spiral wound type membrane element by sealing the liquid in the pressure vessel and dipping the spiral wound type membrane element in the liquid. Thus, the spiral wound type membrane module can be reliably and stably run. Such an operation can be readily performed with no requirement for particular equipment and the contaminants can be separated with no chemical for washing, and hence the method can be carried out at a low cost.
These and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.